Process for producing manganese dioxide for dry cells

ABSTRACT

MANGANESE DIOXIDE IS PRODUCED BY DIRECT CURRENT ELECTROLYSIS OF AQUEOUS SULFURIC ACID SOLUTION OF MANGANESE SULFATE UNDER SPECIFIED CONDITIONS. MN3+ IONS ARE PRODUCED AND ARE HYDROLYZED WITH THE FORMATION OF MNO2.

Nov. 7, 1972 HIDEHISA YAMAGISHI T PROCESS FOR PRODUCING MANGANESE DIOXIDE FOR DRY CELLS Filed Aug. 21, 1970 FIG. 2

FIG.

FIG. 3

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United States Patent Filed Aug. 21, 1970, Ser. No. 66,048 Claims priority, application Japan, Aug. 25, 1969, 44/ 66,556 Int. Cl. B01k 1/00; C01b 15/04 US. Cl. 204-83 6 Claims ABSTRACT OF THE DISCLOSURE Manganesse dioxide is produced by direct current electrolysis of aqueous sulfuric acid solution of manganese sulfate under specified conditions. Mn ions are produced and are hydrolyzed with the formation of MnO The present invention relates to a process for produc* ing manganese dioxide by D.C. electrolysis of an aqueous sulfuric solution of manganese sulfate, wherein it comprises maintaining the anodic current density high, and also the concentration of sulfuric acid high, maintaining the temperature of electrolyte relatively high, so as to carry out hydrolysis of Mn ion produced thereby, forming relatively coarse particles of MnO and filtering it thereafter, heating the MnO thus obtained in electrolyte, thus producing Mn0 simply, inexpensively and efficiently, which has an excellent property as a depolarizer for dry cells, and at the same time, to utilize the filtrate produced after the filtration of Mn0 for leaching manganese (as Mn SO from suitable raw material.

Heretofore, it has been well known to obtain manganese dioxide as the depolarizer for dry cells by D.C. electrolysis of a manganese sulfate solution, which comprises producing manganese dioxide, and applying thereon a washing and other after-treatments. The process of the production is as follows.

The electrolysis is carried out by a process, with conditions including: composition of electrolyte by 20-150 g./ liter of MnSO, and 15-80 g./liter of H 80 temperature of electrolysis, above room temperature (for example: 30-100 C.); current density, 1-2 a./dm. depositing manganese dioxide in lump form on the anode (usually graphite or lead, sometimes titanium), then stripping it off from the anode, and to obtain the product by subjecting the material with trituration or other aftertreatments, Another process is disclosed in Japanese patent application No. 1,696/1966 (published on Feb. 2, 1966), that is, the electrolysis is carried out at conditions: the composition of electrolyte, 10-30 g./liter of Mn and 100-350 g./liter of free H 80 temperature, 10-30 C. (preferably 20 C. or below); current density, 35.5-59.2 a./dm. electrolytically oxidizing Mn ions and hydrolyzing Mn formed thereby, depositing granular MnO filtering and washing the product. A process has been proposed to use, by recirculating, the waste liquid from electrolysis for leaching of ores. However, since the former process is a batch type electrolysis and the current density is low, the productivity is low. In the 3,702,287 Patented Nov. 7, 1972 latter process, the exothermic phenomenon is conspicuous because of the high current load, and it becomes necessary to dissipate the heat, so that a large capacity cooling device is required in order to maintain the specified temperature of 10-30 C. (preferably below 20 C.) especially under a weather condition as in Japan, especially in summer. Thus, the amount of production per unit electrolytic cell becomes small as it is limited by the cooling capacity, so that it is not economical. Moreover, the product MnO obtained by this process has a low purity and a large content of combined Water, so that it has less favorable characteristics as a depolarizer for dry cells.

In the case where the manganese is leached as a sulfate from manganese-bearing containing ores, and when the raw material is in a form of oxides (Mn O or MnO), it is necessary to add heat to effect solution to obtain a sufiicient reaction rate.

Next, an oxidizing agent is added to the solution to remove impurities, especially metals (for example, Fe, etc.), contained in the raw material, to change Fe into Fe then it is necessary to precipitate the metals of impurities as hydroxides, such as Fe(OH) by filtration and separation in regulating the pH about 5. However, there were disadvantages that, when the solution is heated and regulated to have a pH of about 5, Mn ions are hydrolyzed rapidly, producing a yellowish brown colloidal lump which is difiicult to filter, and there is a loss of electrical energy required for oxidizing Mn into Mn ions, so that the current density is decreased.

The object of the present invention is to overcome and improve the above-mentioned disadvantages of conventional processes, and specifically, to deposit Mn0 in the electrolyte by selecting the above described electrolytic conditions. Namely, the invention is to provide a process for obtaining manganese dioxide for dry cells comprising, selecting operational conditions as: composition of electrolyte Mn 10-40 g./liter; free H 400-600 g./ liter; temperature, 30-50 C.; anodic current density, 30-75 a./dm. anode being made of lead, lead alloy or lead oxide (for example, pure PbO' produced by electrodeposition), electrolyzing by D.C. while agitating solution to oxidize Mn so that 5-15 g./ liter of Mn is contained in the electrolyte, carrying out a hydrolyzing reaction gradually according to the following formula:

so as to produce MnO in the electrolyte, and to efiect aftertreatments such as filtering, washing, drying, etc.

The further object of the present invention is to provide a process of producing efficiently manganese dioxide having an excellent discharge characteristic which comprises heating and agitating an electrolyte (containing Mn and free H 80 having said concentration, 5-15 g./ liter of Mn produced by the electrolysis and MnO produced by hydrolysis of Mn) taken out of the electrolytic cell at a temperature of about 50-100 C. for 0.5-4 hrs., to obtain the product after filtering, washing, and drying the MnO or heating the electrolyte after filtering the produced MnO' from said electrolyte so as to convert Mn contained in the solution almost up to MnO filtering it and adding MnO which has been filtered first to this electrolyte which contains almost no Mn (containing 0.1-0.7 gL/Iiter of Mn) by said heating and filtering, heatingv it while substantially returning MnO formed by heating of Mn to the electrolytic cell, subjecting the product after-treatments such as filtering, washing, drying,

etc.

Here, temperature is determined at 3050 C., because it requires a large capacity of cooling device in order to maintain a temperature less than 30 C., taking the temperature rise due to exothermic effect at the electrolysis into consideration. Accordingly the yield per electrolytic cell is restricted, and when the temperature is above 50 C., MnO; is liable to adhere on the surface of the anode which prevents the formationof Mn t ions, leading to a sudden decrease in current efiiciency, and at the same time, brown-colored, minute particles are produced which are not appropriate for depolarizer for dry cells. The reason for selecting the anodic current density at 3075 a./dm. is that, with the density below 30 a./dm. the-productivity is low, and with the density more than 75 a./dm. the current conducting members are overheated due to heavy current load and thatminute particles are produced which are not adequate for depolarizer for dry cells.

With a free H 80 concentration below 4.00 g./liter, Mn is deposited at the anode when the temperature reaches to 30 C., and which decreases in the currentefficiency, thus it is not satisfactory.

When Mn0 is heated in the electrolyte, the heating temperature is limited to 50100 C. and the period is limited to 0.5-4 hours. This is because, with heating conditions with a temperature of below 50 C. and heating time below 0.5 hour, it is not possible to obtain an improvement in the purity of MnO due to oxidation of lower oxides, nor an improvement in the characteristics of the product as a depolarizer. While with a heating condition of a temperature above 100 C. and the heating time more than 4 hours, the oxidation of the lower oxides does not proceed in proportion to the increase in temperature and time, so that the improvement in the characteristic of the product as a depolarizer cannot "be expected.

The invention will now be described referring to the drawings, in which: Y i 1 FIG. 1 is a flow diagram showing the process for production of manganese dioxide according to the process of the present invention; a

FIG. 2 is a graph showing the relation-between the heating temperature when MnO is heated in the solution and the content of the combined'water of MnO jf FIG. 3 is a graph showing the relation of t heating temperature and purity of MnO FIG. 4 is a graph showing the relation between the heating temperature and the content of lower oxide in MnO and i FIG. 5 is a graph showing the relation between the heating time and the content of lower oxide in'MnO In the drawings the broken lines show the'courseof the ofliquid,slurry,etc. raw material and MnO while thefull lines show the Referring to FIG. 1, the raw material and aqueous sill furic solution of manganese sulfate to be u sed as'a circulating acid are introduced in a leaching tank 1, to leach manganese component from the raw material. The manganese sulfate solution is supplied continuously to the electrolytic cell 2, and the DLC. electrolysis is carried out under agitation at a specified temperature. Mn is oxidized electrolytically to Mu -,1, and is hy-v drolyzed gradually, and MnO is deposited in the electro-. lyte.

Slurry containing MnO and Mn ions is continuously discharged from the electrolytic cell 2, and the slurry is filtered by a filter to separate it into- MnO and the filtrate. The filtrate contains Mn at. highconcentration together with H 80 and Mn, the major part of which are returned to the cell 2, and a portion thereof is heated in a heat-treatment tank 4, hydrolyzing Mn to produce MnO filtering it in a filter 5, returning the produced MnO to the electrolytic cell 2, which is used as seed, and the filtrate is passed to the heat-treatment tank 6. In some cases, the filtrate of'the filter 3 is passed directly to the heat-treatment tank 6. MnO obtained on the filter 3 is passed to the heat-treatment tank 6 and (the solution containing the filtrate from the filter 5, which contains H 50 Mn and whose Mn concentration is decreased to about the equilibrium state by, heating), is heated together with the filtrate from the filter 3 or after which filtering it by a filter 7 and separate it into MnO and the filtrate.

MnO is subjected-to treatments such as neutralizing and washing 8, drying 9, etc., and is made into a product. The filtrate from 7 contatins free sulfuric acid, Mn. and low concentration Mn but it is returned to the leaching tank 1, and is used for leaching manganese from the raw material as a circulating acid.

Considered from the thermo-economical point of view, the heat required for heating 4 of the filtrate containing high concentration Mn 7 after separation 3 of MnOg discharged" from the electrolytic cell 2 can be utilized for heating of MnO in the following heat-treatment tank 6, and the heat required for heating the latter may be utilized effectively for leaching manganese portion from the raw material in the next leaching tank 1.

FIG. 2 is a graph showing a relation between the heating temperature and the content of combined water when MnO is heated in electrolyte. When the content of the combined water is decreased by heating it at a temperature more than 100 C. in air for a long time, the performance is deteriorated as a depolarizer for dry cells, but when the content of the combined water is decreased by aheating in a solution as shown in FIG. 2, the de-v polarizing capacity is remarkablyimproved. FIG. 3 is a graph showing a relation between the heating temperature and the purity of MnO and it shows that the purity is increased as the heating temperature is increased. FIG. 4 is a graph showing a relation between the heating temperature and the content of lower oxide in MnO and 7 FIG. 5 is a graph showing a relation between the heating time and the quantity of lower oxide in MnO They show that the content of the lower oxide is decreased as heating temperature is'increased, as well as heating time is increased.

some examples' are given inthe following:

EXAMPLE I (A) Electrolysis Electrolytic cell: .4 liters Electrode:

Anode: Pure PbO formed by electro-deposition Cathode: Grapite I Distatnce between electrodes: 9 mm.

g./ liter (B) Heating after electrolysis Heating temperature: 95 C.

Heating time: 2 hours Electrolyte used for heating contained 400 g./liter of H 2O g./liter of Mn and 0.3 g./liter of Mn (C) Current efficiency and composition of MnO produced Current efiiciency: 76.0%, 6 hours of electrolysis Product:

Total Mn: 58.6% M110 87.9% Combined water: 7.0% Pb: 0.009% Crystal structure: 'y-MnO EXAMPLE II (A) Electrolysis Electrolytic cell, electrodes and the distance between electrodes are the same as in Example I. Composition of electrolyte:

Concentration of free sulfuric acid: 500 g./liter Concentration of Mn: 16 g./ liter Temperature: 45 C. Current density: 60 a./dm. Mean bath voltage: 4.3 v. Material: MnSO, solution containing 110 g./ liter as Mn,

obtained by leaching MnCO Quantity of raw material supplied: 240 ml./ hr. continuous feeding (B) Heating afterelectrolysis Heating temperature: 70 C.

Heating time: 3 hours Electrolyte used for heating contained 500 g./Iiter of H 80 16 g./liter of Mn and 9.5 g./liter of Mn (C) Current eliiciency and composition of MnO produced Current efficiency: 71.2%, 24 hrs. of electrolysis Product:

Total Mn: 58.0%

MnO z 86.4%

Combined water: 9.8% Crystal structure: y-MnO and a small amount of a-MnO EXAMPLE III (A) Electrolysis Same cell as in Example I Electrodes: Both anode and cathode are made of Pb Distance between electrodes: 14 mm.

Composition of electrolyte, the same as in Example I Temperature: 40 C.

Current density: 50 a./dm.

Mean bath voltage: 3.9 v. I

Material: MnSO, solution containing 100 g./liter as Mn,

obtained by leaching MnO Quantity of raw material supplied: 210 ml./hr., continuous feeding (B) Heating after electrolysis Heating temperature: 80 C. Heating time: 1.5 hrs. Electrolyte used for heating is the same as Example I (C) Current efliciency and composition of MnO produced Current eiiiciency: 73.5%, 48 hrs. of electrolysis Product:

Total Mn: 58.3%

MnO z 87.0%

Combined water: 7.5% Crystal structure: 'y-Mno and a small quantity of a-MnO 6 EXAMPLE 1v TABLE I.DI SCHARGB PERFORMANCE Minutes 1 Commercial electrolytic M1102 215 Mn0 produced by Japanese patent publication No.

1696/66 200 MnO produced according to the process of the present invention 250 1(igurntion of closed-clrcult at a voltage of more than As stated above, the effect or advantages of the present invention shown in the examples can be summarized as follows:

Since the temperature selected is high such as 30-50" C., no cooling device is needed for electrolyte, and it is easy to maintain the temperature constant. By heating MnO produced by the electrolysis in the electrolyte having said composition, there were obtained a decrease in the quantity of combined water, increase in purity of MnO decrease in lower oxide as shown in FIGS. 2-5; the duration of closed-circuit at a voltage of more than 1.0 v. is increased jabout 1520% as compared with the conventional products, thus MnO having remarkably excellent characteristics as a depolarizer was obtained. Moreover, by this heating, Mn ions contained in the solution are decomposed and deposited as MnO and through which Mn ions remaining in the solution can be lowered up to the, equilibrium concentration, so that even when the solution is used for leaching of manganese from the raw inaterial, the loss of electric energy due to hydrolysis of Mn ions, and therefore the decrease in current efficiency can be restricted to a minimum. Also, by adopting a series of procedures shown in FIG. 1, the heat required for heating the electrolyte, containing high concentration Mn after separation of MnO discharged from electrolytic cell, can be utilized for heating of Mn0 in the following electrolyte, and the heat required for heating MnO in said electrolyte can be utilized eifectively for leaching manganese from the raw material, respectively.

What is claimed' is:

1. In an electrolytic process for producing manganese dioxide suitable for dry cells wherein direct current electrolysis is employed, the improvement which comprises conducting said electrolysis with an electrolyte containing a concentration of from 10 to 40 grams per liter of Mn+ ion and from 400 to 600 grams per liter of free H a temperature of from 330 C. to 50 C., and an anodic current density'of from 30 to 75 a./dm. to oxidize Mn+ therein to Mn+ and hydrolyzing the resulting product containing Mn to form MnO- in the electrolyte.

2. Process of claim 1, wherein said resulting product contains from 5 to 15 grams per liter of Mn.

3. Process of claim 1, wherein said electrolyte containing Mn0 is heated at a temperature of from 50 C. to C. for from 0.5 hour to 4 hours.

4. Process of claim 2, wherein said electrolyte containing Mn0 is heated at a temperature of from 50 C. to 100 C. for from 0.5 hour to 1 hour.

5. Process of claim 1, wherein MnO is separated from the electrolyte containing Mn0 and is returned to said electrolysis.

6. Process of claim 1, wherein MnO 1) is filtered from the electrolyte containing MnO the resulting filtrate is heated and fine crystals of MnO (2) are filtered therefrom and are returned to said electrolysis; and

7 8 MnO (1) is heated at a temperature of from 50 C. to 2,500,039. v 3/,1960 -Magoffin 'et a1." 204-83 100 C. for from 0.5 hour to 4 hours in the filtrate, 0b- 3,533,924 10/1970 Ve 204-67 tained by filtration of MnO (2).

JOHN: H. MACK, Primary Examiner References Cited I 5 D. R. VALENTINE, Assistant Examiner UNITED STATES PATENTS 3,065,155 11/1962 Welsh 204-83 1,874,827 8/1932 Storey -204 s3 

